Method of calibrating a lithographic apparatus and device manufacturing method

ABSTRACT

In calibration of overlay performance of an immersion lithographic apparatus, two sets of overlay data are obtained from exposures carried out using normal and reversed meanders. The two data sets can then be used to eliminate effects due to wafer cooling.

FIELD

The present invention relates to a method of calibrating a lithographicapparatus and a method for manufacturing a device using the calibratedapparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective numerical aperture (NA) of thesystem and also increasing the depth of focus.) Other immersion liquidshave been proposed, including water with solid particles (e.g. quartz)suspended therein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see for example United States patent U.S. Pat. No.4,509,852, hereby incorporated in its entirety by reference) means thatthere is a large body of liquid that must be accelerated during ascanning exposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application no. WO 99/49504, herebyincorporated in its entirety by reference. As illustrated in FIGS. 2 and3, liquid is supplied by at least one inlet IN onto the substrate,preferably along the direction of movement of the substrate relative tothe final element, and is removed by at least one outlet OUT afterhaving passed under the projection system. That is, as the substrate isscanned beneath the element in a −X direction, liquid is supplied at the+X side of the element and taken up at the −X side. FIG. 2 shows thearrangement schematically in which liquid is supplied via inlet IN andis taken up on the other side of the element by outlet OUT which isconnected to a low pressure source. In the illustration of FIG. 2 theliquid is supplied along the direction of movement of the substraterelative to the final element, though this does not need to be the case.Various orientations and numbers of in- and out-lets positioned aroundthe final element are possible, one example is illustrated in FIG. 3 inwhich four sets of an inlet with an outlet on either side are providedin a regular pattern around the final element.

All lithographic apparatus require at least some calibration before useand the higher the resolution of the apparatus, in general, the morecalibration steps will be required to get the best possible performancefrom the apparatus. An important performance measure of a lithographicapparatus is its overlay performance, which measures the ability of theapparatus to image a pattern on a substrate at a desired positionrelative to an existing pattern on the substrate. Overlay errors may becaused by a variety of causes, for example systematic errors ininterferometric position or displacement measuring systems. To calibratethe overlay performance of a lithographic apparatus, a series of teststructures are printed, normally across the whole of a substrate, andthe position of the test structures is measured. The test structuresmay, for example, be alignment markers so that their positions can bemeasured using an alignment tool provided in the apparatus, or may beoverlay sensitive structures, such as box-in-box markers, wherebyoverlay errors can be directly measured using a known off-line tool. Theresult is a map of overlay errors across the area of a substrate whichcan be used to calibrate the apparatus, e.g. by using them as offsetswhen positioning the substrate during production exposures.

SUMMARY

However, it has been determined that in an immersion lithographyapparatus, that is a lithography apparatus in which at least part of thespace between the final element of the projection system and thesubstrate is filled with a high-refractive index liquid, some overlayerrors are caused by substrate cooling effects. As such these errors arenot only dependent on position but also on the history of the testexposure sequence. Thus, if overlay errors measured in the conventionalway are used to calibrate the apparatus, overlay errors will not beeliminated and may indeed be made worse.

Accordingly, it would be advantageous, for example, to provide animproved method of calibrating a lithographic apparatus.

According to an aspect of the invention, there is provided a method ofcalibrating a lithographic projection apparatus having a projectionsystem, the method comprising:

printing a first set of test structures on a substrate, the substratetraveling a first course relative to the projection system to effect theprinting of the first set of test structures;

printing a second set of test structures on a substrate, the substratetraveling a second course relative to the projection system to effectthe printing of the second set of test structures, the second coursebeing different than the first course;

measuring positional errors in the first set of test structures toobtain a first set of position error data;

measuring positional errors in the second set of test structures toobtain a second set of position error data;

calculating a third set of position error data from the first and secondsets of position error data; and

calibrating the lithographic projection apparatus using the third set ofposition error data.

According to an aspect of the invention, there is provided a devicemanufacturing method using a lithographic projection having a projectionsystem, the method comprising:

calibrating the lithographic projection apparatus by:

printing a first set of test structures on a substrate, the substratetraveling a first course relative to the projection system to effect theprinting of the first set of test structures;

printing a second set of test structures on a substrate, the substratetraveling a second course relative to the projection system to effectthe printing of the second set of test structures, the second coursebeing different than the first course;

measuring positional errors in the first set of test structures toobtain a first set of position error data;

measuring positional errors in the second set of test structures toobtain a second set of position error data;

calculating a third set of position error data from the first and secondsets of position error data;

calibrating the lithographic projection apparatus using the third set ofposition error data; and

using the lithographic apparatus to print device patterns on substrates.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus usable in an embodiment of theinvention;

FIGS. 2 and 3 depict a conventional liquid supply system for use in alithographic projection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 6 depicts a first set of overlay error data obtained in carryingout an embodiment of the invention;

FIG. 7 depicts a third set of overlay error data obtained in carryingout an embodiment of the invention;

FIG. 8 depicts a normal meander path;

FIG. 9 depicts a meander path traveled in the opposite direction; and

FIG. 10 is a flow chart of a method according to the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus usable in anembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam PB (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PLconfigured to project a pattern imparted to the radiation beam PB bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam PB passes through the projection system PL, which focusesthe beam onto a target portion C of the substrate W. An immersion hoodIH, which is described further below, supplies immersion liquid to aspace between the final element of the projection system PL and thesubstrate W.

With the aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved-accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam PB.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe mask MA with respect to the path of the radiation beam PB, e.g.after mechanical retrieval from a mask library, or during a scan. Ingeneral, movement of the mask table MT may be realized with the aid of along-stroke module (coarse positioning) and a short-stroke module (finepositioning), which form part of the first positioner PM. Similarly,movement of the substrate table WT may be realized using a long-strokemodule and a short-stroke module, which form part of the secondpositioner PW. In the case of a stepper (as opposed to a scanner) themask table MT may be connected to a short-stroke actuator only, or maybe fixed. Mask MA and substrate W may be aligned using mask alignmentmarks M1, M2 and substrate alignment marks P1, P2. Although thesubstrate alignment marks as illustrated occupy dedicated targetportions, they may be located in spaces between target portions (theseare known as scribe-lane alignment marks). Similarly, in situations inwhich more than one die is provided on the mask MA, the mask alignmentmarks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and outlets OUT can be arranged in a plate with a hole in itscenter and through which the projection beam is projected. Liquid issupplied by one groove inlet IN on one side of the projection system PLand removed by a plurality of discrete outlets OUT on the other side ofthe projection system PL, causing a flow of a thin film of liquidbetween the projection system PL and the substrate W. The choice ofwhich combination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a seal member which extends along at least a part of aboundary of the space between the final element of the projection systemand the substrate table. Such a solution is illustrated in FIG. 5. Theseal member is substantially stationary relative to the projectionsystem in the XY plane though there may be some relative movement in theZ direction (in the direction of the optical axis). A seal is formedbetween the seal member and the surface of the substrate.

Referring to FIG. 5, reservoir 10 forms a contactless seal to thesubstrate around the image field of the projection system so that liquidis confined to fill a space between the substrate surface and the finalelement of the projection system. The reservoir is formed by a sealmember 12 positioned below and surrounding the final element of theprojection system PL. Liquid is brought into the space below theprojection system and within the seal member 12. The seal member 12extends a little above the final element of the projection system andthe liquid level rises above the final element so that a buffer ofliquid is provided. The seal member 12 has an inner periphery that atthe upper end, in an embodiment, closely conforms to the shape of theprojection system or the final element thereof and may, e.g., be round.At the bottom, the inner periphery closely conforms to the shape of theimage field, e.g., rectangular though this need not be the case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the seal member 12 and the surface of the substrate W. The gasseal is formed by gas, e.g. air or synthetic air but, in an embodiment,N₂ or another inert gas, provided under pressure via inlet 15 to the gapbetween seal member 12 and substrate and extracted via first outlet 14.The overpressure on the gas inlet 15, vacuum level on the first outlet14 and geometry of the gap are arranged so that there is a high-velocitygas flow inwards that confines the liquid. Such a system is disclosed inUnited States patent application no. U.S. Ser. No. 10/705,783, herebyincorporated in its entirety by reference.

Some overlay errors of immersion-type lithographic projection apparatusare due to thermal effects, especially the cooling of the substrate dueto evaporation of residual immersion liquid, e.g. water, left on atarget portion after it has been exposed through the immersion liquid.These errors are not solely position dependent, as are some othersystematic overlay errors in lithographic apparatus, but also depend onthe history of exposures of the substrate—the course (path anddirection) and speed of the substrate during the preceding exposures.

This is confirmed by FIGS. 6 and 7, which show experimental dataobtained from a finite element analysis simulating thermal effects. Inparticular, FIG. 6 depicts overlay error data resulting from thermaleffects caused by the cooling of the substrate due to the passage of thesubstrate under a liquid supply system, especially due to theevaporation of residual immersion liquid, e.g. water, from the substrateafter printing of a target portion. The data simulates results ofcarrying out a normal meander scan, as depicted in FIG. 8, starting atthe bottom left of the wafer. A similar set of data simulating areversed meander scan shown in FIG. 9, starting in the top right of thewafer and following the same course in reverse, was obtained. FIG. 7shows the result of subtracting these two sets of data, from which asignificant change can be seen, allowing identification, and henceseparate correction, of wafer cooling related overlay errors.

From FIG. 7 it can be concluded that by obtaining overlay error datafrom scans carried out in opposite directions, overlay errors resultingfrom thermal effects and dependent on exposure history can be identifiedand hence separated from other systematic and random errors. Calibrationof the apparatus can then be performed using only the systematic errors,leading to increased accuracy.

A flowchart of a method according to the invention is given in FIG. 10.A first substrate is exposed S1 while traveling along a first coursewith a first set of test structures, for example overlay-sensitivemarkers or markers such as alignment markers whose position can beeasily determined, and measured S2 to obtain a first set of error data,which may be overlay data or position data that can be processed tooverlay data. A second set of test structures, preferably identical tothe first set, is then exposed S3 onto the same or a different substrateusing a second course different to the first course, which was used toexpose the first set of test structures. The second set of structuresare then measured to obtain a second set of error data.

In a particular embodiment the first test structures are printed in apredetermined order—the first row (bottom) is printed, e.g., left toright and subsequent rows are printed in alternating directions to forma so-called meander pattern. In a scanner, that is a lithographicapparatus in which each target portion is printed whilst the substrateand pattern are scanned relative to the projection lens, successivetarget portions are scanned in opposite directions, due to the need tobe at full scanning speed at the beginning of each scan and to stop andreverse the mask (if used) between target portions. Thus an additionalback-and-forth movement of the substrate is superimposed on the meanderpath. For clarity, this movement has been omitted from FIGS. 8 and 9.

For each target portion of the exposure of the second set of teststructures, the same scanning direction can be used as for thecorresponding target portion of the first set of test structures. Thisensures that intra-target portion cooling effects are the same,assisting in isolation of the global (whole substrate) cooling effects.Alternatively, the scanning direction for each target portion can bereversed between the first and second test structures, with or withoutreversal of the overall meander. Performing multiple sets ofmeasurements with various different combinations of changes to theexposure order and scan direction can enable isolation, and hencecompensation for, various different forms of local and global coolingeffects.

The course used for the second set of test structures may be opposite inthe sense that it follows the same path but in the opposite direction(time reversal), that it is a mirror image of the first course in aplane perpendicular to the substrate or that it is a rotation of thefirst course about an axis passing though the center of the substrate,or a combination of these. The second course should be traveled at thesame speed as the first course.

Exposure and measurement of the first and second sets of test structuresmay take place in either order and measurements may be taken in parallelwith exposures if the measurements are taken using a stand-alone tool orat the measurement station of a dual stage apparatus. The first andsecond sets of test structures may be exposed and measured a pluralityof times on the same or different substrates and the results averaged toreduce the effect of random errors.

The first and second error data are then processed S5 to obtain a thirdset of error data that can be used in calibration S6 of the apparatusbefore production exposure S7 are performed. The processing of the firstand second data sets to obtain the third data set may be a simplesubtraction of the two data sets or a more complex calculation,dependent on the exact form of the thermal overlay errors expected.

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, where applicable, the invention may takethe form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein.

The present invention can be applied to any immersion lithographyapparatus, in particular, but not exclusively, those types mentionedabove. The immersion liquid used in the apparatus may have differentcompositions, according to the desired properties and the wavelength ofexposure radiation used. For an exposure wavelength of 193 nm, ultrapure water or water-based compositions may be used and for this reasonthe immersion liquid is sometimes referred to as water and water-relatedterms such as hydrophilic, hydrophobic, humidity, etc. may be used.However, it is to be understood that embodiments of the presentinvention may be used with other types of liquid in which case suchwater-related terms should be considered replaced by equivalent termsrelating to the immersion liquid used.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A method of calibrating a lithographic projection apparatus having aprojection system, the method comprising: printing a first set of teststructures on a substrate, the substrate traveling a first courserelative to the projection system to effect the printing of the firstset of test structures; printing a second set of test structures on asubstrate, the substrate traveling a second course relative to theprojection system to effect the printing of the second set of teststructures, the second course being different than the first course;measuring positional errors in the first set of test structures toobtain a first set of position error data; measuring positional errorsin the second set of test structures to obtain a second set of positionerror data; calculating a third set of position error data from thefirst and second sets of position error data; and calibrating thelithographic projection apparatus using the third set of position errordata.
 2. A method according to claim 1 wherein the first and second teststructures are printed in a series of target portions arranged in aplurality of rows on said substrate, the first test structures areprinted by printing the target portions in a predetermined order and thesecond test structures are printed by printing the target portions in anorder that is the reverse of the predetermined order.
 3. A methodaccording to claim 2 wherein each target portion is printed by scanningthe substrate relative to the projection system in a respective scandirection, which may differ from target portion to target portion, andfor each target portion the same scan direction is used for printing thefirst and second test structures.
 4. A method according to claim 2wherein each target portion is printed by scanning the substraterelative to the projection system in a respective scan direction, whichmay differ from target portion to target portion, and for each targetportion opposite scan directions are used for printing the first andsecond test structures.
 5. A method according to claim 3 furthercomprising printing a third set of test structures on each of saidtarget portions in an order that is the reverse of the predeterminedorder and using respective scanning directions that are opposite to thescanning directions used to print the first and second set of teststructures.
 6. A method according to claim 1 wherein the first coursecomprises a meander path along which the first substrate travels in afirst direction and the second course comprises the meander path alongwhich the second substrate travels in a second direction opposite to thefirst direction.
 7. A method according to claim 1 wherein the secondcourse is substantially the same as a mirror image of the first course.8. A method according to claim 1 wherein the second course issubstantially the same as a rotation by 180° of the first course.
 9. Amethod according to claim 1 wherein calculating the third set ofpositional error data comprises taking a difference between the firstand second sets of position error data.
 10. A method according to claim1 wherein the printing of the first and second sets of test structuresand the measuring of positional errors therein are each repeated aplurality of times to obtain the first and second sets of positionalerror data.
 11. A method according to claim 1 wherein the first andsecond test structures are printed on the same substrate.
 12. A methodaccording to claim 1 wherein the first and second test structures areprinted on different substrates.
 13. A method according to claim 1wherein the lithographic projection apparatus is of an immersion type.14. A method according to claim 1 wherein the first and second sets ofpositional error data are sets of overlay error data.
 15. A devicemanufacturing method using a lithographic projection having a projectionsystem, the method comprising: calibrating the lithographic projectionapparatus by: printing a first set of test structures on a substrate,the substrate traveling a first course relative to the projection systemto effect the printing of the first set of test structures; printing asecond set of test structures on a substrate, the substrate traveling asecond course relative to the projection system to effect the printingof the second set of test structures, the second course being differentthan the first course; measuring positional errors in the first set oftest structures to obtain a first set of position error data; measuringpositional errors in the second set of test structures to obtain asecond set of position error data; calculating a third set of positionerror data from the first and second sets of position error data;calibrating the lithographic projection apparatus using the third set ofposition error data; and using the lithographic apparatus to printdevice patterns on substrates.
 16. A method according to claim 15wherein the first and second test structures are printed in a series oftarget portions arranged in a plurality of rows on said substrate, thefirst test structures are printed by printing the target portions in apredetermined order and the second test structures are printed byprinting the target portions in an order that is the reverse of thepredetermined order.
 17. A method according to claim 16 wherein eachtarget portion is printed by scanning the substrate relative to theprojection system in a respective scan direction, which may differ fromtarget portion to target portion, and for each target portion the samescan direction is used for printing the first and second teststructures.
 18. A method according to claim 16 wherein each targetportion is printed by scanning the substrate relative to the projectionsystem in a respective scan direction, which may differ from targetportion to target portion, and for each target portion opposite scandirections are used for printing the first and second test structures.19. A method according to claim 17 further comprising printing a thirdset of test structures on each of said target portions in an order thatis the reverse of the predetermined order and using respective scanningdirections that are opposite to the scanning directions used to printthe first and second set of test structures.
 20. A method according toclaim 15 wherein calculating the third set of positional error datacomprises taking a difference between the first and second sets ofposition error data.
 21. A method according to claim 15 wherein theprinting of the first and second sets of test structures and themeasuring of positional errors therein are each repeated a plurality oftimes to obtain the first and second sets of positional error data. 22.A method according to claim 15 wherein the first and second teststructures are printed on the same substrate.
 23. A method according toclaim 15 wherein the first and second test structures are printed ondifferent substrates.
 24. A method according to claim 15 wherein thelithographic projection apparatus is of an immersion type.
 25. A methodaccording to claim 15 wherein the first and second sets of positionalerror data are sets of overlay error data.